Author: Dr. Kesava Reddy , Dr. Renuka Prasanna, Dr.Prasanna.
College of Dental Sciences, Pavilion Road, Davangere -577004, Karnataka.
ABSTRACT:
Stability of an implant is essential for optimal oral implant function. Therefore osseointegration must be verified when the abutments are connected to the fixtures and before fabricating the prosthesis. The quantity and quality of bone formed during osseointegration is of utmost importance in determining the holding power of an implant, however, failures do occur. These failures can occur early in the healing process or after initial bone remodeling or when the new bone growth has taken place. The ability to detect implants that are failing or will fail is not possible at this time. Osseointegration is basically a histological concept and partially clinical and radiological. It can be difficult to evaluate the state of implant integration only by manual testing of mobility or use of radiology. There are several methods to evaluate the bone-implant interface like mobility, percussion, periotest, resonance frequency analysis with their own merits and demerits. Therefore a quantitative and reproducible measuring system for the detection of fixture mobility is advantageous for determining slight early movements of the implant and the damping capacity of surrounding bone.
INTRODUCTION:
The term osseointegration has been used to define a direct structural and functional connection between ordered living bone and the surface of a load carrying implant. There is good histological evidence to show that following implant placement, healing occurs with the formation of bone in intimate contact with the implant surface. The clinical measurement of implant stability and osseointegration is important to be able to assess success and yet it is largely empirical and subjective in nature1.
Clinically it is possible that an implant may fail in a number of ways; as a result of trauma, infection, placement in compromised tissues or in function due to overloading. Failure may manifest in a number of ways; by an increasing, progressive mobility of the implant, by a decrease in the height of the surrounding marginal bone or by fracture of one or more implant components1. The methods currently available to assess the quality of the implant/tissue interface clinically are invasive and non invasive. Invasive methods are histological, removal torque, cutting torque and Non Invasive methods are mobility, percussion, radiography, periotest, modal analysis hammer, high frequency mechanical vibration, resonance frequency analysis. Invasive methods like the amount of torque required to remove an implant, is a destructive method therefore it is not applicable for clinical assessment. Cutting torque measurement, a clinical method that uses cutting resistance measurements during threading of implants has been used. Although this technique provides an assessment of bone quality at the time of placement, it does not allow for any direct measurement of the changes that occur to the supporting bone over time.
REVIEW AND DISCUSSION:
MOBILITY:
Mobility of the individual implant can be determined by the usual clinical methods like percussing an implant with blunt instrument such as mirror handle and trying to elicit any mobility by moving the fixture. A two point scale is all that is required to mention mobility or non-mobility. Mobility requires the presence of a connective tissue capsule surrounding the implant 2.
Limitations:
More precise determination as to whether implants are osseointegrated or not could be achieved if the prosthesis is detached to test the individual implant stability. However such an approach is regarded as time consuming and cumbersome for the patient. Furthermore, annual removal of crown or bridges could imply additional wear of the components 3.
PERCUSSION:
An additional test is to tap the implant with an instrument. If the tap elicits a solid ring, indicates there is no mobility, but if the sound is dull the implant is presumed not to be osseointegrated and therefore surrounded by fibrous tissue 1.
RADIOGRAPHY:
The radiograph can be used to monitor implant progress, during the first year after fixture insertion; fixtures occasionally fail to integrate with surrounding bone. In some instances this is indicated by clinical signs and symptoms but in absence of clinical conditions radiographs show a more or less wide radiolucency around fixtures(perifixtural radiolucency) indicating that they are not osseointegrated 1,3.
Limitations:
The periapical radiograph gives a two-dimensional image that is only useful to evaluate the mesial and distal surfaces of the implant. No information is provided about the status of the buccal and lingual aspects. Thus, a considerable portion of the surface of the implant is not available for evaluation and regions not osseointegrated may escape detection 3.
To make existence of a soft tissue layer adjacent to the fixture surface radiographically evident, it has to be wide enough to overcome the limitations imposed by the resolution of the radiographic system3.
In addition, anatomical structures surrounding the soft tissue layer and projected on to the same part of the film may conceal it. One can therefore expect false negative diagnoses when fixtures are radiographically evaluated with respect to their integration in surrounding bone tissue. Early signs of integration failures are subtle and hence often radiographically invisible, clinical signs, such as dull note on percussion and persistent discomfort for the patient, may be evident long before the radiographic signs of peri implant radiolucency appear3.
PERIOTEST:
The periotest device is a microcomputerised dynamic measuring tool invented by Schulte and coworkers. This instrument is reported to be able to generate reproducible percussive forces that can be used in measuring the damping ability of periodontium and peri implant tissue. An electronically controlled rod weighing 8g taps the implant four times per second at a constant speed. As result of the impact between the tapping rod and the implant, the rod is decelerated. The greater the stability of the implant, the shorter the contact time and thus higher the damping effect or stiffness of the surrounding tissue. The contact time per impact between rod and the tooth or implant lies in the range of a millisecond and represents the real measuring parameter it is this contact time that represents the measuring parameter for the device. The periotest value (PTV), based on a numerical scale from -8 to +50. Lower the periotest values shorter the contact time and higher the damping which would indicate a corticalisation of the surrounding bone, the range for successful implants has been reported as -5 to +5 4,5 .
Uses: Periotest method can be a very useful clinical parameter to identify, after a regular healing period, those implants that despite being immobile are not stable enough for loading. Because of poor bone quality, immature bone, or not enough bone contact at the interface, full loading of these implants would involve a high risk of load related failure. On the contrary leaving them temporarily unloaded or sub loaded could allow the formation of a mature interface for later use. Periotest measurements after second stage surgery may help the clinician to identify failed implants that are border line i.e. with a very thin fibrous capsule and those in which digital testing for mobility or intra oral radiography may not be sensitive enough to detect problems 4.
Limitations:
There are several factors that limit diagnostic reliability of the periotest instrument to detect changes in peri implant tissues.
The most fundamental issue regarding the diagnostic precision of the periotest instrument is whether the signals correspond to the degree of osseointegration 5. The technique is sensitive to angle, height of / on abutment, angulation of the hand piece and distance the hand piece is held from implant 5. Another potential difficulty is the lack of sensitivity with which the periotest can discriminate between an osseointegrated fixture and a non-integrated fixture 2.
RESONANCE FREQUENCY ANALYSIS [RFA]:
Meredith et al described a non-invasive method whereby bone formation around an implant could be studied in vivo by measuring the resonance frequency of a small transducer attached to an implant fixture. The principle of the method is to attach a transducer either directly to an implanted fixture or via a transmucosal abutment using a screw and the transducer is vibrated1.
Types:
Two commercially available RFA devices have been developed to detect implant stability. The original (electronic) method uses a direct connection (wire) between the transducer and the resonance frequency analyzer. The second uses magnetic frequencies between the transducer (magnetic peg) and the resonance frequency analyzer. The resonance frequency is seen as a peak in an amplitude- frequency plot of the response of the transducer beam and expressed in Hertz. The values are transformed to Implant Stability Quotient units (ISQ) which is used to describe the implant stability. A value of 1 – 100 is obtained, where 1 is lowest and 100 is highest degree of stability 6,7.
Uses: In RFA it is the transducer that vibrates and not the implant. Transducer is designed to resonate in the sonic range and the amplitude of vibration is very small so stresses applied to implant – tissue interface will be negligible 1. RFA measurements have documented healing changes along the implant bone interface by measuring the increase or decrease in stiffness of implant in surrounding tissues 6. RFA is also used to determine whether implants are sufficiently stable to receive the final restoration / to be loaded/ to identify the at risk implants 6.
CONCLUSION:
There is a clearly perceived need for a quantitative method to measure implant stability. Such a measurement may enable the bone quality and primary implant stability to be assessed at the time of fixture placement providing a baseline measurement and an indication of an appropriate healing period.
REFERENCES:
IMPLANT STABILITY
College of Dental Sciences, Pavilion Road, Davangere -577004, Karnataka.
ABSTRACT:
Stability of an implant is essential for optimal oral implant function. Therefore osseointegration must be verified when the abutments are connected to the fixtures and before fabricating the prosthesis. The quantity and quality of bone formed during osseointegration is of utmost importance in determining the holding power of an implant, however, failures do occur. These failures can occur early in the healing process or after initial bone remodeling or when the new bone growth has taken place. The ability to detect implants that are failing or will fail is not possible at this time. Osseointegration is basically a histological concept and partially clinical and radiological. It can be difficult to evaluate the state of implant integration only by manual testing of mobility or use of radiology. There are several methods to evaluate the bone-implant interface like mobility, percussion, periotest, resonance frequency analysis with their own merits and demerits. Therefore a quantitative and reproducible measuring system for the detection of fixture mobility is advantageous for determining slight early movements of the implant and the damping capacity of surrounding bone.
INTRODUCTION:
The term osseointegration has been used to define a direct structural and functional connection between ordered living bone and the surface of a load carrying implant. There is good histological evidence to show that following implant placement, healing occurs with the formation of bone in intimate contact with the implant surface. The clinical measurement of implant stability and osseointegration is important to be able to assess success and yet it is largely empirical and subjective in nature1.
Clinically it is possible that an implant may fail in a number of ways; as a result of trauma, infection, placement in compromised tissues or in function due to overloading. Failure may manifest in a number of ways; by an increasing, progressive mobility of the implant, by a decrease in the height of the surrounding marginal bone or by fracture of one or more implant components1. The methods currently available to assess the quality of the implant/tissue interface clinically are invasive and non invasive. Invasive methods are histological, removal torque, cutting torque and Non Invasive methods are mobility, percussion, radiography, periotest, modal analysis hammer, high frequency mechanical vibration, resonance frequency analysis. Invasive methods like the amount of torque required to remove an implant, is a destructive method therefore it is not applicable for clinical assessment. Cutting torque measurement, a clinical method that uses cutting resistance measurements during threading of implants has been used. Although this technique provides an assessment of bone quality at the time of placement, it does not allow for any direct measurement of the changes that occur to the supporting bone over time.
 |
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| PERIOTEST - ORAL | PERIOTEST DEVICE |
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| RFA - ELECTRONIC TRANSDUCER | RFA - MAGNETIC TRANSDUCER |
REVIEW AND DISCUSSION:
MOBILITY:
Mobility of the individual implant can be determined by the usual clinical methods like percussing an implant with blunt instrument such as mirror handle and trying to elicit any mobility by moving the fixture. A two point scale is all that is required to mention mobility or non-mobility. Mobility requires the presence of a connective tissue capsule surrounding the implant 2.
Limitations:
More precise determination as to whether implants are osseointegrated or not could be achieved if the prosthesis is detached to test the individual implant stability. However such an approach is regarded as time consuming and cumbersome for the patient. Furthermore, annual removal of crown or bridges could imply additional wear of the components 3.
PERCUSSION:
An additional test is to tap the implant with an instrument. If the tap elicits a solid ring, indicates there is no mobility, but if the sound is dull the implant is presumed not to be osseointegrated and therefore surrounded by fibrous tissue 1.
RADIOGRAPHY:
The radiograph can be used to monitor implant progress, during the first year after fixture insertion; fixtures occasionally fail to integrate with surrounding bone. In some instances this is indicated by clinical signs and symptoms but in absence of clinical conditions radiographs show a more or less wide radiolucency around fixtures(perifixtural radiolucency) indicating that they are not osseointegrated 1,3.
Limitations:
The periapical radiograph gives a two-dimensional image that is only useful to evaluate the mesial and distal surfaces of the implant. No information is provided about the status of the buccal and lingual aspects. Thus, a considerable portion of the surface of the implant is not available for evaluation and regions not osseointegrated may escape detection 3.
To make existence of a soft tissue layer adjacent to the fixture surface radiographically evident, it has to be wide enough to overcome the limitations imposed by the resolution of the radiographic system3.
In addition, anatomical structures surrounding the soft tissue layer and projected on to the same part of the film may conceal it. One can therefore expect false negative diagnoses when fixtures are radiographically evaluated with respect to their integration in surrounding bone tissue. Early signs of integration failures are subtle and hence often radiographically invisible, clinical signs, such as dull note on percussion and persistent discomfort for the patient, may be evident long before the radiographic signs of peri implant radiolucency appear3.
PERIOTEST:
The periotest device is a microcomputerised dynamic measuring tool invented by Schulte and coworkers. This instrument is reported to be able to generate reproducible percussive forces that can be used in measuring the damping ability of periodontium and peri implant tissue. An electronically controlled rod weighing 8g taps the implant four times per second at a constant speed. As result of the impact between the tapping rod and the implant, the rod is decelerated. The greater the stability of the implant, the shorter the contact time and thus higher the damping effect or stiffness of the surrounding tissue. The contact time per impact between rod and the tooth or implant lies in the range of a millisecond and represents the real measuring parameter it is this contact time that represents the measuring parameter for the device. The periotest value (PTV), based on a numerical scale from -8 to +50. Lower the periotest values shorter the contact time and higher the damping which would indicate a corticalisation of the surrounding bone, the range for successful implants has been reported as -5 to +5 4,5 .
Uses: Periotest method can be a very useful clinical parameter to identify, after a regular healing period, those implants that despite being immobile are not stable enough for loading. Because of poor bone quality, immature bone, or not enough bone contact at the interface, full loading of these implants would involve a high risk of load related failure. On the contrary leaving them temporarily unloaded or sub loaded could allow the formation of a mature interface for later use. Periotest measurements after second stage surgery may help the clinician to identify failed implants that are border line i.e. with a very thin fibrous capsule and those in which digital testing for mobility or intra oral radiography may not be sensitive enough to detect problems 4.
Limitations:
There are several factors that limit diagnostic reliability of the periotest instrument to detect changes in peri implant tissues.
The most fundamental issue regarding the diagnostic precision of the periotest instrument is whether the signals correspond to the degree of osseointegration 5. The technique is sensitive to angle, height of / on abutment, angulation of the hand piece and distance the hand piece is held from implant 5. Another potential difficulty is the lack of sensitivity with which the periotest can discriminate between an osseointegrated fixture and a non-integrated fixture 2.
RESONANCE FREQUENCY ANALYSIS [RFA]:
Meredith et al described a non-invasive method whereby bone formation around an implant could be studied in vivo by measuring the resonance frequency of a small transducer attached to an implant fixture. The principle of the method is to attach a transducer either directly to an implanted fixture or via a transmucosal abutment using a screw and the transducer is vibrated1.
Types:
Two commercially available RFA devices have been developed to detect implant stability. The original (electronic) method uses a direct connection (wire) between the transducer and the resonance frequency analyzer. The second uses magnetic frequencies between the transducer (magnetic peg) and the resonance frequency analyzer. The resonance frequency is seen as a peak in an amplitude- frequency plot of the response of the transducer beam and expressed in Hertz. The values are transformed to Implant Stability Quotient units (ISQ) which is used to describe the implant stability. A value of 1 – 100 is obtained, where 1 is lowest and 100 is highest degree of stability 6,7.
Uses: In RFA it is the transducer that vibrates and not the implant. Transducer is designed to resonate in the sonic range and the amplitude of vibration is very small so stresses applied to implant – tissue interface will be negligible 1. RFA measurements have documented healing changes along the implant bone interface by measuring the increase or decrease in stiffness of implant in surrounding tissues 6. RFA is also used to determine whether implants are sufficiently stable to receive the final restoration / to be loaded/ to identify the at risk implants 6.
CONCLUSION:
There is a clearly perceived need for a quantitative method to measure implant stability. Such a measurement may enable the bone quality and primary implant stability to be assessed at the time of fixture placement providing a baseline measurement and an indication of an appropriate healing period.
REFERENCES:
- Meredith N, Alleyne D, Cawley P. Quantative determination of the stability of the implant-tissue interface using resonance frequency analysis. Clin Oral Impl Res 1996; 7: 261-67.
- Meredith N, Book K, Friberg B, Jemt T, Sennerby L. Resonance frequency measurement of implant stability in vivo. A cross-sectional and longitudinal study of resonance frequency measurements on implants in the edentulous and partially edentulous maxilla. Clin Oral Impl Res 1997; 8:226-33.
- Sunden S, Grondahl K, Grondahl H-G. Accuracy and precision in radiographic diagnosis of clinical instability in Branemark dental implants. Clin Oral Impl Res 1995; 6:220-26.
- Olive J, Aparicio C. The periotest method as a measure of osseointegrated oral implant stability. Int J Oral Maxillofac Implants 1990; 5:390-400.
- Derhami K, Woolfaardt JF, Dent M, Faulkner G, Grace M. Assessment of the periotest device in baseline mobility measurements of craniofacial implants. Int J Maxillofac Implants 1995; 10:221-29.
- Valderrama P, Oates TW, Jones AA, Simpson J, Schoolfield JD, Cochran DL. Evaluation of two different resonance frequency devices to detect implant stability. A clinical trial. J Periodontal 2007; 78:262-72.
- Glauser R, Sennerby L, Ree A, Lundgren A, Gottlow J. Hammerle CHF. Resonance frequency analysis of implants subjected to immediate or early functional occlusal loading successful vs. failing implants. Clin Oral Impl Res 2004; 15:428-434.
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